Photoresponsive polymers are being found to have several advantageous applications. Photoactivation can be used to control various polymer properties such as release or capture of additives, light activated bending, modulation of refractive index, or phase behavior. Some photoresponsive polymers are photodegradable, wherein photoactivation causes polymer backbone scission, thus decreasing the environmental burden of products made by such polymers. Photodegradable copolymers of vinylic monomers and carbon monoxide are commercially available and are used mostly in agricultural applications. In addition, over the past decade or so several photodegradable polymers have been designed, including polymers containing in-chain metal-metal bonds, photolabile dendrimers, and copolymers of methymethacrylate.
Currently there is a strong need in biomedical applications for polymers that are both photodegradable and biodegradable. Polymers with such properties would be responsive to photochemical input and at a later stage undergo hydrolysis in an aqueous biological environment. Such materials are being investigated as drug delivery devices and as platforms with photo-tunable physical and mechanical properties. Anseth et al have proposed nitrobenzyl ether based PEG hydrogel systems whose moduli and the resultant effect on cell behavior can be tuned by photoirradiation (Kloxin, A. M.; Kasko, A. M.; Salinas, C. N.; Anseth, K. S. Science 2009, 324, 59). Kasko et al. have synthesized hydrogels that are amenable to creating positive and negative features by two photon irradiation (Wong, D. Y.; Griffin, D. R.; Reed, J.; Kasko, A. M. Macromolecules 2010, 43, 2824). Zhao et al. reported a micellar system from nitrobenzyl ether based polyurethanes that degrades upon photoirradiation (Han, D. H.; Tong, X.; Zhao, Y. Macromolecules 2011, 44, 437). Almutairi has reported a quinone methide nanoparticle system that upon light activation results in a cascade of cyclization and rearrangement reactions resulting in degradation of the polymer ((a) Almutairi et al., A. Macromolecules 2011, 44, 8590, (b) Fomina et al. A. J Am Chem Soc 2010, 132, 9540). These examples point to the advantages of photoresponsive polymers. The present invention adds to this general portfolio of photoactive materials to address the increasing need for photoresponsive materials.